Sound Waves on Distant Star Reveal Sun-Like Cycle

Astronomers
studying sound waves on a distant star have discovered that it has a magnetic
cycle similar to our sun's solar cycle.

The find
marks the first time astronomers have detected a star's magnetic cycle using a
method called stellar seismology, which monitors the vibrations
inside a star. The result could help researchers learn more about the inner
workings and evolution of stars, including our own sun.

"This
is one piece of a larger puzzle that should help us better understand the
sun," said study co-author Travis Metcalfe of the National Center for
Atmospheric Research in Boulder, Colo.

Sound on
an alien star

The research
team, led by Rafael Garcia of the Center for Nuclear Studies in Saclay, France,
examined a star known as HD49933. The star is about 100 light-years from Earth
in the constellation Monoceros, and is20 percent more massive than the sun.

Using the
CoRoT (COnvection ROtation and planetary Transits) satellite, the astronomers
measured the star's acoustic fluctuations, which CoRoT
detected as slight variations in light intensity. By analyzing the vibrations,
the researchers were able to map out some key details of HD49933's magnetic
activity cycle.

"Essentially,
the star is ringing like a bell," Metcalfe said in statement. "As it
moves through its starspot cycle, the tone and volume of the ringing changes in
a very specific pattern, moving to higher tones with lower volume at the peak
of its magnetic cycle."

Astronomers
have observed magnetic cycles in other stars before. But they had never done so
using stellar seismology, which should prove to be a powerful tool going
forward.

"This
technique of listening to the stars will allow us to examine potentially
hundreds of stars," said study co-author Savita Mathur, also of the
National Center for Atmospheric Research, in a statement.

Very
short star cycle

The
researchers detected "starspots" on HD49933's surface, areas of
intense magnetic activity analogous to sunspots. And they found that the star's
magnetic activity cycle lasts less than a year. Past surveys of stars have
found cycles similar to the sun's 11-year one.

HD49933's
short cycle should be intriguing to scientists because it may enable them to
observe an entire cycle more quickly. Scientists could thus glean more
information about magnetic patterns than they could by observing parts of a
longer cycle.

"We're
hoping short cycles turn out to be common, so we'll be able to see a full cycle
in lots of stars," Metcalfe told SPACE.com.

The Next
Step

If
scientists can observe many stars' magnetic cycles, they might be able to
recognize general patterns and figure out what's causing them. This information
could shed light on the magnetic processes that go on within the sun,
furthering our understanding of its influence on Earth's climate.

Such
data may also lead to better predictions of the solar cycle and resulting
geomagnetic storms that can cause
major disruption to power grids and communication networks.

"Getting
a general sense of space weather is a very useful thing," Metcalfe said.
"When we only have one star ? the sun ? to look at, we risk getting a
biased view."

And the
researchers may soon be able to start getting such a general sense of space
weather. They plan to monitor the sound waves of more stars, using both CoRoT
and NASA's Kepler
space observatory, which was launched in March 2009.

Metcalfe
is particularly excited about what Kepler ? which will provide continuous data
over three to five years from hundreds of stars ? may be able to show them.

"Kepler
is an unblinking eye," he said. "It's going to be looking for years
at a time, and that's very powerful."

The team
reports its findings in the Aug. 26 issue of the journal Science.